The present invention relates to a semiconductor device and a method of manufacturing the device, in particular, a semiconductor device having a photoelectric conversion element and a method of manufacturing the device.
Semiconductor imaging devices such as CCD (charge coupled device) image sensor and CMOS (complementary metal oxide semiconductor) image sensor are required to have a high S/N ratio in order to supply a high image quality. This means that an increase in S (signal) needs a high saturated signal level and a high sensitivity to light signals, while a decrease in N (noise) needs a low dark current value.
In the above-mentioned semiconductor imaging devices, an increase in efficiency of collecting electrons, obtained by photoelectric conversion of an incident light, in a photoelectric conversion element is necessary for enhancing the sensitivity to input signals. Particularly, light signals in a long wavelength region are however likely to penetrate in a pixel region and hard to cause photoelectric conversion, which may deteriorate the efficiency of the photoelectric conversion element to collect the light.
In addition, when the light supplied to one photoelectric conversion element and penetrating deeply in a pixel region is photoelectrically converted when it reaches, for example, a substrate of a semiconductor imaging device, there is a possibility of photoelectrically converted electrons leaking into, for example, another photoelectric conversion element adjacent to the one photoelectric conversion element via the substrate. Also when light signals of a level exceeding the saturated signal level are input, there is a possibility of electrons leaking into another photoelectric conversion element adjacent to the one photoelectric conversion element to which the light signals are input. Such leakage of electrons, that is, so-called blooming, if any, deteriorates the electron detection sensitivity of the one photoelectric conversion element and for detecting excess electrons, increases noise in the detection signal, leading to a reduction in S/N ratio.
A technology for suppressing such a phenomenon is disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2008-91781 (Patent Document 1), Japanese Unexamined Patent Application Publication No. 2007-13177 (Patent Document 2), and Japanese Unexamined Patent Application Publication No. 2008-98601 (Japanese Patent 3).